The present invention relates to a method and a device for controlling an output variable of a drive unit in the starting phase.
In the wake of more stringent vehicle emission regulations, there have also been attempts to optimize the starting phase of an internal combustion engine. The starting phase of an engine includes the operating phase from turning the ignition switch to running the engine at a steady-state idling speed. It has been found that there is a correlation between hydrocarbon emissions (untreated HC emissions) and the extent of speed overshoot in the starting phase. Speed overshoot in this connection denotes overshooting of the speed within the starting phase beyond the steady-state idling speed assumed subsequently without actuation of the accelerator pedal by the driver. In general, untreated HC emissions increase with the extent of the speed overshoot. The reason for this increase in untreated HC emissions is the evaporation or breakaway of wall film components of the fuel. This effect is intensified by the drop in manifold pressure and the increase in air flow with a speed overshoot. There is thus a demand for optimization of the starting phase, in particular optimization of the speed characteristic, which should be flat and robust and have minimal overshoot.
It is known from German Published Patent Application No. 199 39 821 that during the starting phase of an engine, at least one parameter of an idling speed controller may be adapted specifically to the conditions of the starting phase. It is proposed in particular that when the steady-state speed setpoint to be maintained subsequently is exceeded due to manipulation of the firing angle, the speed overshoot be limited by manipulating the firing angle, the firing angle intervention being based on a parameter of the idling speed controller provided specifically for the starting phase. This procedure yields an effective reduction in speed overshoot, but it has the potential for further optimization with regard to untreated HC emission.
German Patent Published Application No. 196 18 893(U.S. Pat. No. 6,000,376) describes a torque-based engine control in which a torque setpoint is determined for adjusting the filling (air supply) to the engine on the basis of a predetermined torque setpoint derived from the deflection of the accelerator pedal or predetermined by other control systems. At least one additional torque setpoint is determined and implemented for adjustment via a more rapid control parameter of the engine, such as the firing angle or the fuel supply. This permits independent control of filling and the rapid torque intervention path under certain operating situations.
Through regulation of the starting phase on the basis of a time-dependent setpoint curve, a speed overshoot may be omitted or specified in a defined manner without any sacrifice of reliability in starting. In the case of an increased friction moment in startup, the regulation, preferably the idling controller, will detect this on the basis of the deviation between the actual variable and the specified variable and will bring the actual variable closer to the specified variable. The startability of the engine may thus be ensured even under difficult conditions.
By specifying the time characteristic of at least one output variable (e.g., torque, power, speed) of the drive unit in the starting phase, which is started with an actual value of the output variable, when at least one condition is present one achieves the result that the actual variable matches the specified variable when this condition is met. This prevents intervention into a manipulated variable for influencing the output variable. Therefore, operation of the engine during the starting phase may be optimal. This is also true of the remaining ramping-up curve of the speed, because in principle the deviations between the specified value and the actual value of the output variable are also much smaller in this phase, and thus much smaller actuating interventions may be necessary to maintain the specified time characteristic.
Due to the elimination of or definite reduction in the speed overshoot, a startup having lower untreated HC emissions may be guaranteed.
Due to the time-dependent specification of the characteristic of the output variable, integration into a torque-based control structure is possible without any interfering actuating interventions in startup. This regulating method may be especially effective when the controller intervention is implemented via the firing angle of the engine.